廃タイヤパウダーを混合した凍土の工学的性質に関する研究

摘要

Recently big building projects have increased the demand for crushed stone and gravel butthey are hard to secure granular material of fine quality because the government’s strictpolicies of environment and natural conservation have made developing stony mountainsdifficult.This study, aiming at positive, effective use of discarded tire powder as soil material,instead of granular material of good quality in want, conducted a field experiment on the nonmixedand mixed soil (mixing ratio of tire powder 20%) in a concrete basin in order toinvestigate the effect of tire powder on inhibiting frost heave as the first step of the research.At the field experiment, frost heave amount, frozen depth, frost heave force, soil temperature,ground water level, etc. were observed. Also the frost heave suppressing effect of tire powderwas evaluated quantitatively based on frost heave ratio and segregation potential.As the second step of the study, tests of thermal conductivity, unfrozen water, ultrasonicwave and laboratory frost heave, etc. were carried out on the mixed soil of discarded tire toinvestigate its engineering characteristics.First, test of thermal conductivity was carried out to analyze the thermal conductivitybehavior according to temperature variance and mixing ratio using discarded tire powder ofthree different kinds in particle diameter. Besides, using pulsed Nuclear Magnetic Resonance(NMR) equipment, unfrozen water content of frozen soil was measured and expressed intothe function of temperature. Also, by developing two-phase thermal conductivity model ofsoil particle and water for unfrozen soil proposed by Woodside, a new three-phase thermalconductivity model was proposed, consisting of soil particle, ice and unfrozen water, that canbe applied even to the area of frozen soil.For ultrasonic wave test, using pulse method, a kind of nondestructive method that caniievaluate dynamic characteristics of frozen soil, behavior of P wave (dilatational wave) and Swave (shear wave) of frozen soil was analyzed according to the change of -10 degree Celsiusto 0 degree Celsius and mixing ratio of discarded tire powder, and unconfined compressivetest was conducted on four kinds of mixed soil from discarded tire powder. Also, change inunfrozen water of frozen soil mixed with discarded tire powder was analyzed, and therelationships between unfrozen water content and elastic wave velocity as well as betweenelastic wave velocity and unconfined compressive strength were examined. In addition, usingthe measures of elastic wave velocity, against frozen soil mixed with tire powder, elasticconstant, dynamic shear modulus, dynamic elastic modulus and Poisson’s ratio werecalculated.In frost-heave experiment, aiming to examine the frost heave characteristics of mixed-soilaccording to the change of mixing ratio of discarded tire powder and to investigate the relatedfrost heave suppressing mechanism, the author, based on the idea of change in coefficient ofpermeability by the mixture of discarded tire powder, first calculated unsaturated coefficientof permeability from the relationship between unfrozen water content in the low temperaturebelow 0 degree Celsius and unsaturated water content in the normal temperature above 0degree Celsius. Then, after considering the ice-impeding factor and ratio between the crosssections of soil and tire powder in the mixed soil, effect of tire powder reducing frostsusceptibility was systemically investigated through calculating the permeability coefficientof frozen fringe.